mess-model

The purpose of the Agent Based Modelling is to

1. explore how the irrigation-related agents and their related environment interact with each other;
2. test the decision-making mechanisms from individual level and collective level in an irrigation system; and
3. study how short-term irrigation management actions create long-term irrigation system patterns.

The environment of this simulation is a water system: one main river brings water to an irrigation system with farmers with their farmlands, canals, and gates. The model consists of the following entities: river, canals, gates, farmlands, barley, virtual water managers, and farmers. The entities and their state variables are defined as follows:

1. The river is the origin of the water resource. Water moves one cell per time step, whatever the inflow. The relevant variable is varied river discharges.
2. Canals are built along the river. Canals are transfer tools of water, transporting water from the river to farmers. Water moves one cell per time step, organized with canal capacity.
3. Gates allow water to flow from the river into irrigation canals, and from canals to farm(s). There are gates at the junction of the river and canals or two canals (head gates), and at the junction of canals and farms (farmers’ gate). Gates control the water flow – either from river to canals or from canals to farmers. Water moves one cell per time step, arranged by gate capacity.
4. There are two types of farmlands in IRABMs: one farmland type is with barley; another one is fallow – preparing for the next crop season. The farmlands with barley have the variables: water demand, water stress, start barley, barley yields, harvest cycle, barley alive or not. The fallow farmlands have the variable: available for barley sowing, pre-irrigation demand when they are ready for the next cultivation.
5. Virtual water managers propose water (re)allocation strategies. Water allocation control, or irrigation water control, to canals, can be done in two ways – time control and demand control (IRABM). In AIRABM, water managers can redistribute water among farmers along the same canal, while water managers can control the irrigation system dynamics based on the harvest situation in IRABM3 as well. Water distribution strategies are shaped through river discharge, gate capacity, the number of canals irrigated simultaneously, and barley water demands.
6. The farmers make choices on crop growing and sowing choice in the next year (farmlands dynamics). Farmers will support the water allocation strategies in the system. They have the variable: irrigation demand.
7. Barley yields update annually and are based on the supplied water throughout the season. Barley yields and farmlands dynamics at farms (the smallest spatial scale, representing individual farmers or families) are used to check results of water distribution, individual farmers’ planting choices, and the collective decision-making on water relocation to upstream, middle stream, and downstream farmers. Aggregating yields at the levels of individual farmers, canals, or whole system allows for exploring how specific irrigation strategies create patterns in water availability and yields. The system dynamics – farmers/canals movement or expansion is used to explore how the short-term actions promote longer-term patterns.